Multiple step-up rectifier circuit

ABSTRACT

A multiple step-up rectifier circuit comprises a transformer, a series circuit of diodes, a first series circuit of capacitors, a second series circuit of capacitors and a third series circuit of capacitors. An AC signal source is connected to the primary winding of the transformer. The secondary winding of the transformer has a tap connected to the ground. The tap is also connected to one end of the series circuit of diodes, so that the diodes are biased in the same direction. The first series circuit of capacitors is connected between both ends of the series circuit of diodes. The second series circuit of capacitors is connected between one end of the secondary winding and a connecting point between the diodes. The third series circuit of capacitors is connected between the other end of the secondary winding and another connecting point between the diodes. A connecting point between the capacitors is also connected to a connecting point between the diodes. Another connecting point between capacitors is connected to another connecting point between the diodes. A third connecting point between the capacitors is connected to yet another connecting point between the diodes.

BACKGROUND OF THE INVENTION

The present invention relates to a multiple step-up rectifier circuitfor rectifying an output voltage from the secondary winding of atransformer, and for boosting that voltage.

Various conventional multiple step-up rectifier circuits have beenproposed. However, output voltages from these conventional circuits arerelatively low. For this reason, the dielectric withstand voltagebetween primary and secondary windings of a transformer used in such arectifier circuit may only be minimal.

Various compact power supply units with high-frequency arrangements havealso been proposed, if only recently. A high-voltage power supply is notexceptional. The size of the high-voltage power supply tends to bedecreased by the high-frequency arrangement. Even if a compacttransformer is manufactured, the insulating gap between the primary andsecondary windings of the transformer does not change, in principle. Forthis reason, linkage inductances of the primary and secondary windingsare increased, depending on the size of the transformer. As a result, itis difficult to effectively induce a high voltage at the secondarywinding. In particular, in a high-voltage transformer, corona dischargemust be decreased to substantially zero, within the range of operatingvoltages, to achieve a long service life and high reliability. However,this is more difficult to achieve when an AC potential differencebetween the primary and secondary windings is increased.

SUMMARY OF THE INVENTION

A primary object of the present invention is to provide a multiplestep-up rectifier circuit which has a simple circuit arrangement and asmall number of circuit elements, and which allows for the generation ofa high voltage using a transformer having a low dielectric withstandvoltage between primary and secondary windings thereof.

To achieve the above object of the present invention, a multiple step-uprectifier circuit is provided, which comprises: a transformer having aprimary winding connected to an AC signal source and a secondary windingwith a tap; a plurality of rectifiers connected in series in such a wayas to be biased in one direction; a plurality of first capacitorsconnected in series between both ends of the series circuit of therectifiers, the connecting points between said first capacitors beingconnected to some of the connecting points between said rectifiers; atleast one second capacitor connected between one end of the secondarywinding of said transformer and one of the connecting points betweensaid rectifiers; and a plurality of third capacitors connected in seriesbetween the other end of the secondary winding of said transformer andone of the connecting points between said rectifiers, the connectingpoints between said first capacitors, said second capacitor and saidthird capacitors being connected to the connecting points between therespective rectifiers.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a circuit diagram of a multiple step-up rectifier circuitaccording to a first embodiment of the present invention;

FIG. 2 is a circuit diagram of a multiple step-up rectifier circuitaccording to a second embodiment of the present invention;

FIG. 3 is a circuit diagram of a multiple step-up rectifier circuitaccording to a third embodiment of the present invention;

FIG. 4 is a circuit diagram of a multiple step-up rectifier circuitaccording to a fourth embodiment of the present invention; and

FIG. 5 is a circuit diagram of a multiple step-up rectifier circuitaccording to a fifth embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

An embodiment of the present invention may now be described withreference to the accompanying drawings.

With reference to FIG. 1, an AC power supply A is connected to theprimary winding n1 of a transformer T. A rectangular AC voltage isapplied from the AC power supply A to the primary winding n1. One end ofthe primary winding n1, a core TC of the transformer T, and a tap m(given as the central point) of a secondary winding n2 are respectivelygrounded. A series of diodes D1 to D6 are connected between the tap mand a connecting point i, in such a way that the diodes D1 to D6 havethe same bias direction. More specifically, the anode of the diode D1 isconnected to the tap m, and the cathode of the diode D6 is connected tothe connecting point i. A series circuit of first capacitors C11, C12 isconnected between the anode of the diode D1 and the cathode of the diodeD6 (i.e., in parallel with the series circuit of diodes D1 to D6). Theconnecting point between the capacitors C11, C12 is connected to aconnecting point f between the diodes D3, D4. Therefore, the capacitorC11 is connected in parallel to a series circuit of the diodes D1, D2,D3, and the capacitor C12 is connected in parallel to a series circuitof the diodes D4, D5, D6. A series circuit of second capacitors C21, C22is connected in parallel between one output terminal b of the secondarywinding n2 and a connecting point g between the diodes D4, D5. Theconnecting point between the second capacitors C21, C22 is connected toa connecting point d between diodes D1 and D2. Therefore, capacitor C21is connected in parallel to diode D1, and capacitor C22 is connected inparallel to a series circuit of diodes D2, D3 and D4. A series circuitof third capacitors C31 and C32 is connected in parallel between theother output terminal a of the secondary winding n2 and a connectingpoint h between diodes D5 and D6. The connecting point betweencapacitors C31 and C32 is connected to a connecting point e betweendiodes D2 and D3. Finally, the capacitor C31 is connected in parallel toa series circuit of the diodes D1 and D2, and the capacitor C32 isconnected in parallel with a series circuit of the diodes D3, D4 and D5.

The operation of the multiple step-up rectifier having the abovearrangement may be described as follows. A rectangular AC voltage isapplied to the primary winding n1 of the transformer T. Now assume thata voltage of 2E (V) appears across the output terminals a and b of thesecondary winding n2 wherein the output terminal a is set to bepositive. In this case, the capacitor C21 is supplied with a voltage ofE (V) through the diode D1 with the point d positive and the outputterminal b negative. Subsequently, the voltage across the outputterminals a, b of the secondary winding n2 is inverted, and a voltage of2E (V) appears, with output terminal b being positive and outputterminal a being negative. In this case, capacitor C31 is chargedthrough diode D2 with a voltage 3E (V) obtained as the sum of thevoltage of 2E (V) between the output terminals of the secondary windingn2 and the voltage of E (V) charged in the capacitor C21. At this time,point e is set to be positive. When the voltage is inverted again, thecapacitor C11 is charged through the diode D3, with a voltage of 4E (V)being obtained as the sum of the voltage of E (V) between the tap m andthe output terminal a of the secondary winding n2, and the voltage of 3E(V) from the capacitor C31. At this time, point f is positive. At thesame time, the capacitor C21 is charged again with the voltage of E (V)through the diode D1. In this case, the diode D1 is rendered conductive,so that the tap m is set at the same potential as that at point d.Therefore, the capacitor C22 is charged through the diodes D3 and D4with a voltage of 4E (V) in the same manner as in the capacitor C11. Atthis time, the point g is set to be positive. Furthermore, when theoutput voltage from the secondary winding n2 is inverted, the capacitorC31 is charged with a voltage of 3E (V) through the diode D2 in themanner described above. Meanwhile, since the diode D2 is renderedconductive, point e is at the same potential as that of point d.Consequently, the capacitor C32 is charged through the diode D5 with avoltage equal to that at the capacitor C22 (i.e., a voltage of 4E (V)).At this time, point h is positive. When the output voltage from thesecondary winding n2 is inverted, capacitor C21 is charged with avoltage of E (V) through diode D1, capacitor C11 is charged with avoltage of 4E (V) through diode D3, and capacitor C22 is charged with avoltage of 4E (V) through diodes D3 and D4. Meanwhile, since the diodeD3 is rendered conductive, point e is at the same potential as that ofpoint f. As a result, capacitor C12 is charged with a voltage of 4E (V)through diode D6. At this time, the point i is positive. In this manner,every time the voltage from the secondary winding n2 is inverted, theabove operation is repeated. The combined voltages (8E (V)) fromcapacitors C11 and C12 appear at point i.

A multiple step-up rectifier circuit operated as described above has thefollowing effects. No problem occurs in the primary winding n1 when thedielectric withstand voltage of the transformer T is considered, sincethe primary winding n1 receives a low voltage. An AC voltage of ±E (V)is generated from the secondary winding n2 with respect to the groundpotential, so that a voltage of 2E (V) is generated across the outputterminals a and b of the secondary winding n2. It is easy tostructurally separate the output terminals a and b from each other.Furthermore, the separation of the output terminals a and b will notinfluence the electrical characteristics of the transformer T. As aresult, no dielectric problem occurs between output terminals a and b.However, the distance between the primary and secondary windings n1, n2influences magnetic coupling and the dielectric withstand voltagetherebetween which, in turn, has a direct influence on the electricalcharacteristics of the transformer T. According to the presentinvention, the dielectric withstand voltage between the primary andsecondary windings n1, n2 can be held low, in relation to the rectifiedoutput voltage, which is very advantageous.

AC corona discharge, which greatly influences the service life of thetransformer, tends to occur when the distance between the primary andsecondary windings is decreased to efficiently perform electromagneticcoupling, especially in a compact transformer obtained by high-frequencyarrangement. From this viewpoint, the present invention is alsoadvantageous in that the dielectric withstand voltage between theprimary and secondary windings is decreased.

To obtain an output voltage of 20 (kv), a transformer having an ACdielectric withstand voltage of only 2.5 (kv) is required. If aconventional Cockcroft-Walton circuit is used, for a transformer havinga given winding ratio, only four capacitors and four diodes, two-thirdsthe number of those in the circuit of the present invention, arerequired. However, the dielectric withstand voltage of the transformeris twice (5 (kV)) that of the transformer of the present invention.Therefore, if a transformer having a given dielectric withstand voltageis used, eight capacitors and eight diodes, or 4/3 the number of thosein the circuit of the present invention, are required.

From the viewpoint of circuit performance, any circuit of the presentinvention has a smaller voltage drop when compared with aCockcroft-Walton circuit having a transformer with the same dielectricwithstand voltage as that of the transformer of the present inventionunder a given load current. When the step-up ratio of the multiplestep-up is increased, this effect is also increased.

Under a given load current, the ripple component of the conventionalCockcroft-Walton circuit is increased in proportion to the square of astep-up ratio, while the ripple component of the circuit of the presentinvention is increased in proportion to a step-up ratio or a value lessthan this ratio. Therefore, the circuit of the present invention can bedesigned to have a small ripple component when compared with that of theconventional Cockcroft-Walton circuit.

According to the present invention, the dielectric withstand voltage ofthe capacitor is only slightly increased, compared to that of theconventional circuit. However, the shape of the internal elements of thecapacitor is considerably simpler. Capacitors having a high dielectricwithstand voltage are commercially available, which is not the case withtransformers.

As may be seen from the above embodiment, the number of capacitors ordiodes is not limited to six, but may be extended in multiples of 3, toincrease the step-up ratio. This can be achieved by repeating theoperation described above.

FIG. 2 shows a multiple step-up rectifying circuit according to a secondembodiment of the present invention.

The connecting point between capacitors C11 and C12 (FIG. 1) isconnected in the second embodiment to the connecting point g betweendiodes D4 and D5. Other arrangements of the second embodiment aresubstantially the same as those of the first embodiment.

The operation of the circuit having the above arrangement may bedescribed as follows.

A rectangular AC voltage is applied to a primary winding n1 of atransformer T. Now assume that a voltage of 2E (V) appears across outputterminals a and b of a secondary winding n2 such that the outputterminal a is set to be positive. In this case, the capacitor C21 issupplied with a voltage of E (V) and the connecting point d is positive.

Let us now assume that a voltage of 2E (V) occurs between the outputterminals a, b of the secondary winding n2, in such a way that theoutput terminal b is set to be positive. In this case, the capacitor C31is supplied, through diode D2, with a voltage of 3E (V), as a sum of thevoltage of 2E (V) from the output terminals a, b of the secondarywinding n2 and the voltage of E (V) charged in the capacitor C21. Atthis time, connecting point e is positive.

When the voltage across the output terminals a, b of the secondarywinding n2 is re-inverted, the capacitor C21 is charged through diodeD1. In this case, since the diode D1 is rendered conductive, theconnecting point d has the same potential as that of the tap m of thesecondary winding n2. The capacitor C22 is supplied through the diode D3with a voltage of 4E (V) as a sum of the voltage of E (V) across the tapm and the output terminal a of the secondary winding n2 and the voltageof 3E (V) charged on the capacitor C31. At this time, the connectingpoint f is positive.

When the voltage across the output terminals a, b of the secondarywinding n2 is inverted, capacitor C31 is supplied with a voltage of 3E(V), through diode D2. In this condition, since the diode D2 is renderedconductive, point d has the same potential as that of point e.Therefore, the capacitor C32 is supplied through the diodes D4 and D5with a voltage of 4E (V) from the capacitor C22.

Simultaneously, capacitor C11 is supplied, through diode D4, with avoltage of 6E (V), as the sum of the voltage of E (V), which is locatedbetween the tap m and the output terminal b of the secondary winding n2;the voltage of E (V) from the capacitor C21; and the voltage of 4E (V)from the capacitor C22.

When the voltage across the output terminals a, b of the secondarywinding n2 is inverted, capacitors C21 and C22 are supplied withvoltages E (V) and 4E (V), through the diodes D1 and D3, respectively.At the same time, with reference to the tap m of the secondary windingn2, the connecting point h is set at a voltage of 8E (V) which is thesum of voltage E (V) located between the tap m and point a of thesecondary winding of the transformer, voltage 3E (V) from the capacitorC31, and voltage 4E (V) from the capacitor C32. The capacitor C12 issupplied through the diode D6 with a voltage having a difference 2E (V)from the voltage of 6E (V) of the capacitor C11.

Every time the voltage across the output terminals a, b of the secondarywinding n2 is inverted, the above operation is repeated. As a result, asteady voltage of 8E (V) appears at point i, and a steady voltage of 6E(V) appears at point g. The points i and g, respectively, can be used ashigh voltage output terminals.

The same effect obtained in the first embodiment may be obtained by thesecond embodiment.

FIG. 3 shows the basic arrangement of a multiple step-up rectifiercircuit according to a third embodiment of the present invention.

Referring to FIG. 3, capacitor C11 is connected in parallel to a seriescircuit of diodes D1 and D2. Capacitor C12 is connected in parallel to aseries circuit of diodes D3, D4 and D5. One end of capacitor C21 isconnected to an output terminal b of a secondary winding n2, and theother end thereof is connected to a connecting point f between diodes D3and D4. One end of capacitor C31 is connected to an output terminal a ofthe secondary winding n2, and the other end thereof is connected to aconnecting point d between diodes D1 and D2. Capacitor C32 is connectedin parallel to a series circuit of diodes D2, D3 and D4.

The circuit of this embodiment can generate a high voltage output insubstantially the same manner as those of the first and secondembodiments, with the same effect.

One circuit arrangement of the conventional multiple step-up rectifiercircuit was presented in the first to third embodiments. However,according to the present invention, the number of diodes and capacitorscan be considerably changed in accordance with the dielectric withstandvoltage of the capacitor and the number of outputs. Therefore, thenumber of circuit elements can be reduced to a minimum, therebyproviding a highly reliable, low-cost circuit.

FIG. 4 shows a multiple step-up rectifier circuit according to a fourthembodiment of the present invention.

Two ends i, j of six series-connected diodes D1 to D6 are positive andnegative high-voltage output terminals, respectively.

Referring to FIG. 4, the circuit shown therein is substantially the sameas that of FIG. 1, except that an anode of a diode D1 is disconnectedfrom a tap m of a secondary winding n2 and is connected to a connectingpoint j, and a connecting point f between diodes D3 and D4 is grounded.

The operation of the circuit described above may be described asfollows.

Let us assume that a voltage of 2E (V) occurs across the outputterminals a, b of the secondary winding n2, with output terminal a setto be positive. A capacitor C31 is supplied with a voltage E (V) fromthe following closed loop consisting of the output terminal a, capacitorC31, connecting point e, diode D3, connecting point f and tap m. At thistime, the output terminal a is set to be positive.

When the voltage between the output terminals a, b of the secondarywinding n2 is inverted, a voltage of 2E (V) occurs across the terminalsa, b and output terminal b is set to be positive. In this case,capacitor C21 is charged with a voltage of 3E (V), i.e., the sum of thevoltage E (V) from the capacitor C31 and the voltage 2E (V) at thesecondary winding n2. At this time, voltage 3E (V) is supplied to thecapacitor C21, through components which occur in the following order:connecting point d, diode D2, connecting point e, capacitor C31, outputterminal a and output terminal b. The output terminal b is then set tobe positive.

The output voltage at the secondary winding n2 is re-inverted, so that avoltage 2E (V) appears across the output terminals a, b, in such a waythat output terminal a is positive. The capacitor C11 is charged with avoltage of 4E (V) from the closed loop consisting of the connectingpoint j, diode D1, connecting point d, capacitor C21, output terminal b,tap m and connecting point f. This voltage 4E (V) is the sum of thevoltage 3E (V) charged on the capacitor C21 and the voltage E (V)appearing between the output terminal b and the tap m of the secondarywinding n2. At this time, the connecting point f is set to be positive.Simultaneously, the capacitor C22 is charged with a voltage of 4E (V)from the closed loop consisting of the connecting point d, capacitorC21, the connecting point b, tap m, connecting point f, diode D4 andconnecting point g. Meanwhile, the capacitor C31 is supplied with avoltage of E (V) through the closed loop.

The output voltage from the secondary winding n2 is then inverted, and avoltage of 2E (V) is generated in such a way that output terminal b ispositive. In this case, capacitor C32 is charged with a voltage of 4E(V), from the closed loop consisting of connecting point e, capacitorC31, output terminal a, output terminal b, capacitor C21, capacitor C22,connecting point g, diode D5 and connecting point h. The connectingpoint h is then set to be positive. The voltage charged on capacitor C32is obtained by adding a voltage E (V) to capacitor C31, the outputvoltage 2E (V) of the secondary winding n2 and the voltage 4E (V) ofcapacitor C22, to produce a sum of 7E (V); and, then, by subtracting thevoltage 3E (V) on capacitor C21 from that sum. Meanwhile, the capacitorC21 is recharged to a voltage of 3E (V), through the above-mentionedclosed loop.

The output voltage from the secondary winding n2 is again inverted, sothat a voltage of 2E (V) appears across the output terminals a, b, insuch a way that output terminal b is set to be positive. The capacitorC12 is charged through the closed loop consisting of the connectingpoint f, tap m, the output terminal a, capacitor C31, connecting pointe, capacitor C32, connecting point h, diode D6 and connecting point i.In this case, a voltage of 4E (V), obtained by adding the voltage of E(V), appearing across the tap m and output terminal a, and the voltageof 4E (V) from the capacitor C32; and, then, by subtracting the voltageof E (V) from capacitor C31 from the obtained sum, is supplied tocapacitor C12 in such a manner that the connecting point i is set to bepositive. Meanwhile, the capacitor C31 is charged again with a voltageof E (V). Thereafter, every time the output voltage from the secondarywinding n2 of the transformer T is inverted, the operation describedabove is repeated, until a voltage of 4E (V) is supplied to capacitorC11 in such a way that connecting point f is set to be positive, and avoltage of 4E (V) is applied to capacitor C12 in such a way thatconnecting point i is positive. As a result, a voltage +4E (V) occurs atthe connecting point i, and a voltage -4E (V) occurs at the connectingpoint j.

The multiple step-up rectifier circuit having the configurationdescribed above can obtain the same effects as those of the first tothird embodiments.

Furthermore, according to the fourth embodiment, a plurality of positiveand negative outputs can be arbitrarily generated by using a singletransformer. Therefore, a high-voltage power supply for a TWT (travelingwave tube) using a plurality of positive and negative voltages can bereadily arranged by using the circuit of the fourth embodiment. Thisembodiment can also be effectively used for an X-ray power supply whichgenerates a high voltage between the output terminals, with minimumground insulation. For example, according to this embodiment, adielectric ground voltage of 40 (kV) is required to obtain a voltage of80 (kV) between the output terminals when a transformer having adielectric withstand voltage of 10 (kV) is used.

FIG. 5 shows a fifth embodiment of the present invention, which is amodification of the circuit shown in FIG. 4.

With reference to FIG. 5, a connecting point between capacitors C31 andC32 is connected to a connecting point f between diodes D3 and D4. Aconnecting point between capacitors C11 and C12 is connected to aconnecting point e between diodes D2 and D3 and to a tap m of asecondary winding n2 through a power supply B having a voltage E₀ (V).Other parts of the circuit shown in FIG. 5 are the same as those shownin FIG. 4.

According to the circuit described above, capacitor C31 is immediatelysupplied with a voltage of E₀ (V), through diode D3. The capacitor C21is supplied with a voltage E₀ (V) so that point d is set at a positivepotential by the leak current from the diode D2 (this can be completedin 1 or 2 seconds when the capacitance of the capacitor C21 is 0.01(μF), and the resistance of the diode D6 is 100 (MΩ)).

The operation of the fifth embodiment shown in FIG. 5 may be describedas follows. Let us assume that a voltage 2E (V) is generated across thesecondary winding n2, whereby output terminal b is positive. In thiscase, a voltage of E (V) is applied from output terminal b to the tap m,through capacitor C21, connecting point d, diode D2, connecting point eand power supply B. As a result, capacitor C21 is supplied with avoltage of E₀ -E (V), whereby connecting point d is set to be positive.A voltage E (V) is applied from output terminal a to capacitor C31,through tap m, power supply B, connecting point e, diode D3 andconnecting point f. Since the power supply B applies a voltage of E₀(V), the capacitor C31 is supplied with a voltage of E₀ +E (V), wherebythe connecting point f is set to be positive.

Let us assume that a voltage of 2E (V) is generated across the secondarywinding n2 and is then inverted, whereby output terminal a becomespositive. In this case, a voltage of 2E (V) is applied to the capacitorC11 through the closed loop consisting of the connecting point d,capacitor C21 [-(E₀ -E) (V)], connecting point b, tap m, power supply B,capacitor C11 [-2E (V)]and connecting point j, diode D1. Hence, theconnecting point j is set to be positive.

Meanwhile, a voltage of 4E (V) is applied to capacitor C22 through theclosed loop consisting of connecting point d, capacitor C21 [-(E₀ -E)(V)], output terminal b, output terminal a, capacitor C31 [E₀ +E (V)],connecting point f, diode D4, connecting point g and capacitor C22. As aresult, connecting point g is set to be positive.

Suppose a voltage of 2E (V) is further generated and is so appliedacross the secondary winding n2 that output terminal b is positive.Then, a voltage of 4E (V) is applied to the capacitor, through theclosed loop consisting of capacitor C31 [-(E₀ +E) (V)], output terminala, output terminal b, capacitor C21 [E₀ -E (V)], capacitor C22 [4E (V)],connecting point g, diode D5, connecting point h and capacitor C32. Inthis case, connecting point h is set to be positive.

Let us assume that the output voltage from the secondary winding n2 isso inverted that output terminal a becomes positive. In this case, avoltage of 6E (V) is supplied to the capacitor C12 through the closedloop consisting of the power supply B, tap m, output terminal a,capacitor C31, capacitor C32 [4E (V)], connecting point h, diode D6 andcapacitor C12. The connecting point i is set to be positive.Consequently, the voltage between the connecting points j and i rises to8E (V). And the potential difference between the ground and theconnecting point j is E₀ -2E (V), and the potential difference betweenthe ground and the connecting point i is E₀ +6E (V).

The circuit of the fifth embodiment can perform the same function asthose of the first to fourth embodiments.

Furthermore, in a manner similar to that in the second and fifthembodiments, the circuit can be effectively arranged, so that capacitorC11 or C12 may be connected in parallel to a series circuit of at leastfour diodes, to decrease the number of elements, and capacitor C11 orC12 may be connected in parallel to a series circuit of two diodes, toprovide an output voltage margin.

In the first to fifth embodiments, the diodes appear in one biasingdirection. However, the biasing direction may be reversed. In this case,the polarity of charge for each capacitor is inverted, and the outputvoltage and the operations described in the above embodiments can beperformed.

In the above embodiments, the tap m of the transformer T is the centralpoint of the secondary winding. However, the tap m need not be thecentral point, but may be preset to be an arbitrary point. In this case,the dielectric withstand voltage required for the transformer isslightly increased.

According to the present invention, as described in detail above, amultiple step-up rectifier circuit having a simple circuit arrangementand a small number of elements can be provided, wherein a high voltagecan be generated by a transformer having a low dielectric withstandvoltage between the primary and secondary windings.

What is claimed is:
 1. A multiple step-up rectifier circuitcomprising:two output terminals; transformer means having a primarywinding connected to an AC signal source, and a secondary winding with atap; a plurality of rectifying means connected in series, thus forming aseries circuit, and being biased in one direction, the ends of saidseries circuit being connected to said two output terminals,respectively, said two output terminals being isolated from said centertap; a plurality of first capacitive means connected in series betweenthe ends of said series circuit of said rectifying means, the connectingpoints between said first capacitive means being connected to firstconnecting points between said rectifying means, which are other thanthose adjacent to the ends of said series circuit of said rectifyingmeans and are not adjacent to one another; at least one secondcapacitive means connected between one end of the secondary winding ofsaid transformer means and a second connecting point between saidrectifying means; and a plurality of third capacitive means connected inseries between the other end of the secondary winding of saidtransformer means and a third connecting point between said rectifyingmeans, the connecting points between said third capacitive means beingconnected to fourth connecting points, which are not adjacent to oneanother, and to connecting points other than those adjacent to the thirdconnecting point and said tap being coupled to one of the connectingpoints of said first capacitive means.
 2. A circuit according to claim1, wherein a DC power supply is connected between said tap and said oneconnecting point of said first capacitive means.